Its almost as if the Fraunhofer institute is pushing these stories in hopes of getting people to switch to a format that they can still charge money for. But the truth is: while an AAC may sound better at a given bitrate than an MP3, the fact that I can drop a 128 Gb memory card in my phone for $35.00 makes it largely immaterial. Few people can distinguish a 128 bit MP3 from the original recording as it is. And those that claim they can distinguish a 256 bit MP3 track from the uncompressed source are largely just deluding themselves (placebo effect).
There are various app accessible to download YouTube videos as MP3 or any audio format. You can download the Snap Tube Pro app or Tube Mate Pro app. Both are awesome to download videos as audio formats.